The present invention relates in general to measuring instruments, and in particular, to a method and apparatus for ascertaining the gap between opposing parts.
In manufacturing quality control, it is often necessary to verify the width of a gap between two adjacent, opposing surfaces. For example, when servicing a computer printer, it is required to optimally set the distance between an end part of a printing head and a surface of a printing medium in order to obtain high quality printing on the printing medium. This distance is called a print gap. It is, therefore desirable to preset the print gap in accordance with the thickness of the recording medium, such as paper.
Currently, print gaps and similar gaps are measured with a plurality of shim or wire gauges (xe2x80x9cfeelerxe2x80x9d gauges). Feeler gauges are thin steel plates of a predetermined thickness. The width of a gap is measured by a feeler gauge by inserting the gauge into the gap and moving the gauge back and forth within the gap. The amount of frictional resistance between the gauge and the opposing surfaces increases as thicker gauges are inserted into the gap. A gauge that is too thin will result in little or no frictional resistance when inserted into the gap. On the other hand, if the gauge is too thick, insertion will be impossible or will be achieved with great difficulty. Thus, it is possible to determine width of the gap by judging the degree of frictional resistance.
Judging the correct amount of frictional resistance is subjective and is dependent on the experience of the operator. Often an inexperienced operator may not be able to repeat the same result because he is relying on his judgment regarding the correct degree of frictional resistance. Furthermore, other operators may not be able to reproduce the results even with the same gauge.
What is needed, therefore, is an inexpensive device to objectively determine whether a gap has been set to the proper tolerances.
The previously mentioned needs are fulfilled with the present invention. Accordingly, there is provided, in a first form, a feeler gauge which provides an objective means of determining the width of a gap. The feeler gauge comprises a gap measuring element which is insertable into the gap and an indicator coupled to the gap measuring element for automatically indicating when said gap has been set to a predetermined distance. The measuring element comprises two plates which act as a switch in an electrical circuit. When the gap gauge is inserted into a gap of predetermined width, the plates press against each other and current from a power source lights up a light emitting diode. Conversely, when the plates are inserted into a gap that is too wide, the plates do not press against each. The circuit, therefore, is not complete, and the light emitting diode does not light up. Thus, this invention provides an objective, reliable means for confirming the width of a gap. The invention can be used for gaps of different widths by varying the thicknesses of the plates.
These and other features, and advantages, will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only form of the invention.